Hearing aids have adjustable operational parameters that improve the performance of the hearing aid for a specific person or for specific environments. Such adjustable operational parameters include, for example, gain and output. Hearing aids based on analog circuitry may have operational parameters that can be adjusted by a potentiometer. Most analog hearing aids are not programmable. Digital hearing aids, on the other hand, are typically programmable and offer more sophisticated performance. Digital hearing aids often include memory and processor capability and operate based on data stored in the digital hearing aid. The operational parameters of such a digital hearing aid are determined from the stored data, where the data is programmed by software run on a computer coupled to a programming port in the digital hearing aid.
Digital hearing aids are more flexible, sophisticated than analog hearing aids, but require the use of a computer for programming. Hearing aid dispensers may be reluctant to sell digital hearing aids for any number of reasons including:                They may prefer making potentiometer adjustments for the end-user rather than making adjustments by computer.        They may prefer the portability of a screwdriver to the portability of a computer. They may frequently do fittings outside the office and would have to carry a laptop computer around to fit/adjust digital hearing aids.        They may not want to invest in computer equipment for the office.        They may be unfamiliar with and/or intimidated by computers.        
The frequency response of a non-programmable, analog hearing aid is controlled via the adjustment of one or more potentiometers. Adjustment of a potentiometer, or trimpot, requires the use of a small screwdriver designed to fit in the shallow indentation that spans the diameter of the trimpot. A typical trimpot diameter is 0.10″. Rotation of a trimpot in the clockwise or counterclockwise direction causes a continuous change in one or more response characteristics. Examples of parameters typically controlled through trimpot adjustment include gain, output, high pass filter characteristics, and low pass filter characteristics. A response range defines the behavior for a given trimpot. The minimum and maximum of the response range are defined by the points at which the trimpot is rotated fully either clockwise or counter-clockwise, but precise intermediate settings are not specified.
The frequency response of a digital hearing aid is typically controlled via adjustments made on a computer while the hearing aid is connected to it by a cable. The desired response is then saved to the device before it is disconnected from the computer. However, digital hearing aids can also be controlled via the adjustment of potentiometers, as is done with analog devices. The variable resistor inside the potentiometer is connected to an analog to digital (A/D) converter in the hearing aid that converts the voltage across the resistor to a discrete parameter value. The number of discrete values for a given parameter depends on the precision of the A/D converter. A 4-bit A/D converter, for example, will map the full range of trimpot positions to 16 discrete settings. It may be desirable in some cases, however, to be able to make precision adjustments to the hearing aid without the use of a computer.
There exists a need for improved digital hearing aids and improved methods for adjusting the operational parameters of digital hearing aids.